Delivery of tractive force to vehicle wheels must be accomplished as smoothly as possible. For example, launching a vehicle to provide tractive force at the vehicle wheels should be done without abrupt changes in torque that will be noticeable to the vehicle occupants. A fluid coupling such as a torque converter may be used to provide such a “soft-lockup” launch. Torque converters are relatively large, and require a hydraulic supply to operate.
Limited slip differentials allow some angular velocity, also referred to as slip, between vehicle wheels, but lockup at a predetermined slip. A smooth lockup of the limited slip differential will smooth torque spikes to improve passenger comfort.
Traditional clutches have masses attached rotationally to the input member, so that as engine speed rises, so does the torque capacity of the clutch. Such traditional clutches have low torque capacity at idle stall (as engine speed is low). However, these clutches retain high torque capacity when locked, making engagement, disengagement, and shifts noticeable to vehicle passengers unless additional measures are taken to control torque spikes.